The plasma supplemented modified activated clotting time for monitoring of heparinization during cardiopulmonary bypass: a pilot investigation

In vitro thrombogenicity evaluation of rotary blood pumps by thromboelastometry

In vitro thrombogenicity tests for rotary blood pumps (RBPs) could benefit from assessing coagulation kinematics, as RBP design improves. In this feasibility study, we investigated if the method of thromboelastometry (TEM) is able to assess coagulation kinematics under the in vitro conditions of RBP tests. We conducted in vitro thrombogenicity tests (n=4) by placing Deltastream^® DP3 pumps into test loops that were filled with 150 mL of slightly anti-coagulated porcine blood, adjusted to an activated clotting time (ACT) well below clinically recommended levels. Blood samples were taken at certain time points during the experiment until a continuous decrease in pump flow indicated major thrombus formation. Blood samples were analyzed for ACT, platelet count (PLT), and several TEM parameters. While visible thrombus formation was observed in three pumps, ACT indicated an ongoing activation of coagulation, PLT might have indicated platelet consumption. Unexpectedly, most TEM results gave no clear indications. Nonetheless, TEM clotting time obtained by non-anticoagulated and chemically non-activated whole blood (HEPNATEM-CT) appeared to be more sensitive for the activation of coagulation in vitro than ACT, which might be of interest for future pump tests. However, more research regarding standardization of thrombogenicity pump tests is urgently required.

In vitro effects of emicizumab on activated clotting time in blood samples from cardiac surgical patients

BACKGROUND

Heparin management in hemophilia A (HA) patients with a factor VIII (FVIII) inhibitor can be challenging due to severe activated clotting time (ACT) prolongations. It is important to better understand the impact of emicizumab, a FVIII mimetic on ACT, and tissue factor (TF)-based coagulation assays.

METHODS

Whole blood from 18 patients undergoing cardiopulmonary bypass (CPB) were mixed in vitro with pooled normal plasma, FVIII-deficient or FVIII-inhibitor plasma to affect functional FVIII levels. ACTs and heparin concentration by protamine titration were measured in whole blood mixture with/without emicizumab (50-100 μg/ml). Thrombin generation and plasmin generation were measured in the patient's plasma mixed with normal plasma or FVIII-inhibitor plasma to assess the impact of emicizumab under low TF activation.

RESULTS

FVIII inhibitors prolonged ACTs by 2.2-fold compared to those in normal plasma mixture at baseline. During CPB, ACTs in normal plasma mixture, and FVIII-deficient mixture were in 400s, but ACTs reached 900s in FVIII-inhibitor mixture. Emicizumab shortened ACTs by up to 100s in normal plasma mixture, and FVIII-deficient mixtures. ACTs remained over 600s in FVIII-inhibitor mixture, despite adding emicizumab at 100 μg/ml. Heparin concentration measured by TF-based protamine titration was unaffected. Emicizumab enhanced thrombin peak in the presence of FVIII inhibitors, whereas plasmin generation was mainly affected by thrombin generation, and systemic use of ɛ-aminocaproic acid.

CONCLUSIONS

FVIII inhibitors extensively prolong ACTs in heparinized whole blood, and clinical levels of emicizumab partially reverse ACT values. Protamine titration should be considered for optimal heparin monitoring in emicizumab-treated patients with FVIII inhibitors.

Activated Clotting Times Demonstrate Weak Correlation With Heparin Dosing in Adult Extracorporeal Membrane Oxygenation

BACKGROUND

The optimal monitoring strategy for anticoagulation management in extracorporeal membrane oxygenation (ECMO) remains a clinical controversy. The Extracorporeal Life Support Organization Anticoagulation Guidelines suggest that multiple anticoagulation assays may be needed but do not specify a preferred management strategy.

STUDY QUESTION

In adult ECMO patients, which anticoagulation assays demonstrate the highest correlation with unfractionated heparin (UFH) dose requirements?

STUDY DESIGN

We performed a retrospective chart review of adult patients cannulated to ECMO between February 2013 and July 2015.

MEASURES AND OUTCOMES

The primary outcome was the correlation between activated clotting time (ACT), activated partial thromboplastin time (aPTT), and anti-Xa and UFH dose. Secondary outcomes included correlations between anticoagulation assays. Correlations were calculated for the entire cohort, with subgroup analysis of venoarterial and venovenous ECMO patients.

RESULTS

Forty-eight patients were included in the analysis, 26 initially cannulated to venoarterial ECMO and 22 to veno-venous ECMO. The median duration of ECMO therapy was 7 days. Mean UFH requirements were 1149 units/h or 15.3 units/kg/h. Total UFH dose was most correlated with anti-Xa levels (r = 0.467), whereas weight-based heparin dose was most correlated with aPTT (0.405). For correlations between anticoagulation assays, anti-Xa and aPTT were more highly correlated with each other (r = 0.633) compared with ACT.

CONCLUSIONS

In adult patients requiring ECMO, anti-Xa and aPTT monitoring were correlated more closely with UFH dosing than ACT.

Perioperative Coagulation Management of a Hemophilia A Patient During Cardiac Surgery

Perioperative management of cardiovascular surgical procedures requiring cardiopulmonary bypass (CPB) in patients with hemophilia A poses a clinical challenge in coagulation management. Use of CPB requires the administration of an anticoagulant, usually unfractionated heparin, and also causes dilutional coagulopathy, platelet dysfunction or platelet consumption coagulopathy. Hypothermia and activation of the inflammatory cascade also affect coagulation. The effects of CPB on circulating levels of factor VIII have not been clearly defined. In this review, the effects of CPB and hemodilution on FVIII are shown in a case presentation, and perioperative laboratory testing in patients with hemophilia A having cardiac surgery is discussed along with perioperative and postoperative coagulation management.

Anticoagulation management associated with extracorporeal circulation

The use of extracorporeal circulation requires anticoagulation to maintain blood fluidity throughout the circuit, and to prevent thrombotic complications. Additionally, adequate suppression of hemostatic activation avoids the unnecessary consumption of coagulation factors caused by the contact of blood with foreign surfaces. Cardiopulmonary bypass represents the greatest challenge in this regard, necessitating profound levels of anticoagulation during its conduct, but also quick, efficient reversal of this state once the surgical procedure is completed. Although extracorporeal circulation has been around for more than half a century, many questions remain regarding how to best achieve anticoagulation for it. Although unfractionated heparin is the predominant agent used for cardiopulmonary bypass, the amount required and how best to monitor its effects are still unresolved. This review discusses the use of heparin, novel anticoagulants, and the monitoring of anticoagulation during the conduct of cardiopulmonary bypass.

Variability in anticoagulation management of patients on extracorporeal membrane oxygenation: an international survey

OBJECTIVE

The objective of this study was to determine current practices of anticoagulation in patients on extracorporeal membrane oxygenation.

DESIGN

Internet-based cross-sectional survey distributed between November 2010 and May 2011.

SETTING

Extracorporeal Life Support Organization-registered extracorporeal membrane oxygenation centers internationally.

PARTICIPANTS

: Extracorporeal membrane oxy genation medical directors and coordinators.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

There were 121 responses from extracorporeal membrane oxy genation medical directors and coordinators at 187 Extracorporeal Life Support Organization centers with access to the survey. Eighty-four of 117 (72%) respondents reported having a written institutional extracorporeal membrane oxy genation protocol for both anticoagulation and blood product management at their institutions. Sixty-nine of 117 (59%) respondents reported use of tip-to-tip or partially heparin-bonded circuits. Unfractionated heparin was used at all centers; only 8% of respondents indicated use of alternative anticoagulation medications in the six months prior to the survey. The preferred method of anticoagulation monitoring was the serial measurement of activated clotting time, as reported by 97% of respondents. In this survey, 82% of respondents reported antithrombin III testing, 65% reported anti-factor Xa testing, and 43% reported use of thromboelastography during extracorporeal membrane oxy genation. Goal ranges for these three tests and interventions triggered by out-of-range values were found to be variable.

CONCLUSIONS

Extracorporeal membrane oxy genation anticoagulation management policies vary widely by center. The majority of extracorporeal membrane oxy genation programs employ activated clotting time as the preferred anticoagulation monitoring tool. The coagulation system is also monitored using more specific markers such as antithrombin III, anti-factor Xa, and thromboelastography by a large number of centers. Future research is needed to elucidate optimal anticoagulation management and improve outcomes.

Activated clotting time (ACT)

The standard assay for monitoring anticoagulation during extracorporeal life support (ECLS) is the activated clotting time (ACT) test, with celite, kaolin, and glass beads being the most commonly used activators to initiate contact activation. The point-of-care ACT test has been the preferred test in catheterization labs and cardiac theatres because it has a number of advantages over laboratory tests (Spinler et al., Ann Pharmacother 39(7-8):1275-1285, 2005): Shorter time between sampling and results. Smaller blood sample size. Availability to have test performed by non-lab personnel. Reduced errors associated with sample mislabeling/mishandling. Decreased risk of sample degradation with time. There are other coagulation monitoring tests available; however these are usually specific and do not take into account the global picture of the entire clotting system. The standard coagulation tests (prothrombin time (PT), activated partial thromboplastin time, thrombin time (TT), and fibrinogen level) are plasma tests measuring plasma haemostasis and not patient haemostasis. The ACT measurement uses whole blood, thereby incorporating the importance of platelets and phospholipids in the role of coagulation. Many of the problems with the haemostatic system during ECLS are caused by the activation of platelets, which are not detected by standard tests. Because an ACT test is nonspecific there are many variables such as hypothermia, platelets, aprotinin, GP IIb/IIIa antagonists, haemodilution, etc. that can alter its results. For this reason it is important to gain an understanding as to how these variables interact for meaningful interpretation of the ACT test result.

Coagulopathy and hemostatic monitoring in cardiac surgery: an update

OBJECTIVES

Cardiac surgery with cardiopulmonary bypass (CPB) causes severe derangements in the hemostatic system, which in turn puts the patient at risks of microvascular bleeding. Excessive transfusion and surgical re-exploration after cardiac surgery are potentially associated with a number of adverse outcomes including increased mortality.

DESIGN

This review describes coagulopathies occurring in cardiac surgery and the monitoring of these. Viscoelastic hemostatic assays (VHA) have routinely been used in cardiac surgery for more than 25 years and at least 16 studies (involving more than 3250 patients, including three randomized controlled trials) have compared VHA to routine coagulation tests (RCoT) with regards to their ability to predict bleeding and re-do surgery and also with regards to transfusion requirements secondary to hemostatic therapy based on VHA vs. RCoT.

RESULTS

All 16 studies demonstrated superiority with VHA as compared to RCoT both in predicting bleeding and need for re-do surgery and in reducing the total amount of blood transfusions by employing goal-directed administration of blood products based on VHA as compared RCoT based therapy or at the clinicians discretion.

CONCLUSIONS

The different types of coagulopathies observed in patients undergoing cardiac surgery requires adequate and timely hemostatic therapy and real-time monitoring with WHA such as TEG/ROTEM and whole blood platelet aggregometry.

Measurement of activated coagulation time in children: evaluation of the blood-saving kaolin i-STAT activated coagulation time technique in pediatric cardiac anesthesia

OBJECTIVE

To compare the activated coagulation times (ACTs) measured with the blood-saving kaolin i-STAT 1 ACT technique (Abbott Point of Care Inc, Princeton, NJ) with ACTs obtained from the widely used ACTR II device (Medtronic, Inc, Minneapolis, MN) in children undergoing cardiac surgery.

DESIGN

A prospective, observational single-center study.

PARTICIPANTS

Forty-four pediatric cardiac surgery patients.

INTERVENTION

Surgery was performed with cardiopulmonary bypass (CPB) necessitating heparinization.

METHODS AND MAIN RESULTS

ACTs measured on the i-STAT 1 device (2 × 95 μL) were compared with those obtained from the Medtronic ACTR II device (2 × 0.5 mL). Blood samples were drawn before, during, and after heparinization for CPB and paired for statistical analysis. The 2 techniques were compared using simple and multiregression analyses and the Bland-Altman method. In total, 179 intrarater and 142 interrater data pairs were analyzed. The intrarater reliability of the 2 devices was good, with a mean bias and limits of agreement of +2.0 and -55.5/+59.5 seconds for the Medtronic ACTR II and +0.5 and -59.9/+60.9 seconds for the i-STAT 1. An interrater reliability analysis of the mean of simultaneously measured ACT of the Medtronic ACTR II and both i-STAT 1 devices yielded a mean bias of -5.3 seconds and limits of agreement of -210.1/+199.5 seconds. A comparison of the higher of the paired ACT values from both devices showed similar results. After the removal of heparin, the i-STAT 1's ACT values became significantly lower than those measured on the Medtronic ACTR II (p < 0.001). Simple and multiregression analyses revealed that base excess independently influenced the mean bias of the ACT values from the Medtronic ACTR II (p = 0.037) and i-STAT 1 devices (p = 0.036).

CONCLUSION

The kaolin i-STAT 1 ACT technique agreed well with the Medtronic ACTR II technique during the nonheparinized phase that preceded CPB. The overall agreement between the ACT obtained from the 2 devices was poor. The routine use of i-STAT 1 measured ACT values cannot be recommended as a reliable alternative to the Medtronic ACTR II.

Anticoagulation and coagulation management for ECMO

Advances in extracorporeal membrane oxygenation (ECMO) management have helped to reduce complications compared with its inception but they remain high. The principal causes of mortality and morbidity are bleeding and thrombosis. The nonbiologic surface of an extracorporeal circuit provokes a massive inflammatory response leading to consumption and activation of procoagulant and anticoagulant components. The vast differences in neonatal and adult anticoagulation and transfusion requirements demands tremendous clinical knowledge to provide the best care. Increased use of thrombelastogram will complement other methods currently being used to improved care. Methods to recognize the level of thrombin formation at the bedside could help reduce neurologic complications. ECMO requires a multidisciplinary team approach to achieve the best outcomes.

Anticoagulation and Pediatric Extracorporeal Membrane Oxygenation: Impact of Activated Clotting Time and Heparin Dose on Survival

BACKGROUND

Anticoagulation during pediatric extracorporeal membrane oxygenation (ECMO) is accomplished by titrating heparin administration to maintain an activated clotting time (ACT) of between 180 and 220 seconds. We hypothesized that an ACT of 180 to 220 seconds results in inadequate anticoagulation during pediatric ECMO and that increased heparin levels will lead to increased survival.

METHODS

A retrospective review was conducted of 604 consecutive pediatric ECMO patients at a single institution between 1980 and 2001. Multiple logistic regressions were used to assess the impact on survival of ACT, heparin, age, weight, diagnosis, and previous surgery.

RESULTS

There were 349 survivors (57.8%), and 255 (42.2%) nonsurvivors. Mean hours on ECMO were 182 +/- 134 (range, 3 to 957 hours), mean ACT was 227 +/- 50 seconds (range, 158 to 620 seconds), and the mean hourly heparin dose was 45 +/- 21 U/kg (range, 6 to 134 U/kg). Regression analysis indicated that increased heparin administration was predictive of survival (p < 0.0001), independent of all other variables. The ACT was not a predictor of survival (p = 0.096). Although previous surgery was independently associated with an increased likelihood of ECMO death (p < 0.001), increased heparin administration again exerted a survival advantage (p = 0.012).

CONCLUSIONS

Adherence to the recommended ACT of 180 to 220 seconds in pediatric ECMO patients may result in inadequate anticoagulation. Survival is improved by increased heparin administration independent of the ACT. The ACT may be too insensitive to maintain adequate long-term systematic anticoagulation, and other methods, such as heparin levels or functional parameters such as anti-Factor Xa activity or thrombin generation, should be investigated.

Bivalirudin anticoagulation for cardiopulmonary bypass in a patient with heparin-induced thrombocytopenia

PURPOSE

To describe the perioperative management in a heparin-induced thrombocytopenia (HIT) positive patient who had prosthetic valve endocarditis and an aortic root abscess. The patient underwent high-risk cardiac re-operation with the use of the alternative anticoagulant, bivalirudin.

CLINICAL FEATURES

A 62-yr-old patient who underwent stentless tissue aortic valve replacement with a Toronto-SPV valve in 1998, was admitted to hospital with symptoms of stroke. A heparin infusion was started and further investigation revealed positive blood cultures. The patient developed HIT which was confirmed by laboratory tests. Echocardiographic examination performed one month later showed vegetations on the aortic tissue valve and a small aortic root abscess. The patient still tested positively for the presence of HIT antibodies and was treated conservatively with antibiotics. A repeat echocardiographic examination showed progression of the aortic root abscess and it was decided to proceed with urgent redo aortic valve surgery. Anticoagulation for cardiopulmonary bypass (CPB) was achieved with the use of a direct thrombin inhibitor (DTI), bivalirudin. Following an uneventful wean from CPB, hemostasis was achieved within 40 min. The postoperative course was uncomplicated and the patient was discharged from hospital on the seventh postoperative day.

CONCLUSION

Bivalirudin is a DTI, which can be used as an alternative anticoagulant for CPB in HIT positive patients. This case report showed a favourable outcome with bivalirudin for urgent complex redo cardiac surgery requiring CPB.

Measurement of the activated clotting time during cardiopulmonary bypass: differences between Hemotec ACT and Hemochron Jr apparatus

BACKGROUND

Measurement of the activated clotting time (ACT) represents a standard method for coagulatory assessments. The test employs specific agents to trigger the coagulation process. The present study aimed to compare kaolin (Hemotec) versus a combination of silica, kaolin and phospholipid (Hemochron Jr) ACTs.

METHODS

Hemotec and Hemochron Jr ACT monitors were compared by simultaneous measurement of paired arterial blood samples (n = 114) with respect to precision and bias during clinical conditions of cardiopulmonary bypass (CPB). The influence of haemodilution on the ACT was tested in an ex-vivo model.

RESULTS

The precision of Hemotec and Hemochron Jr ACT measurements attained 21 +/- 2.6 s versus 27.0 +/- 2.6 s (p = 0.126) during CPB and 2.5 +/- 2.2 s versus 9.4 +/- 6.9 s (p = 0.000) after protamine administration, respectively. The Hemochron Jr monitor was associated with a bias of -102 +/- 13.7 s compared to the Hemotec ACT monitor (p = 0.000) during CPB and -6.9 +/- 2.9 s after protamine (p = 0.025). Linear regression analysis of ACT readings between monitors reached r = 0.526 (p = 0.000). Hemochron Jr ACT values correlated with the erythrocyte volume fraction r = 0.379 (p = 0.000). Ex-vivo data indicated that the Hemotec ACT monitor was associated with relatively higher ACT readings after haemodilution.

CONCLUSION

The ACT is not a standardized measure. Test results are strongly associated with the specific compounds used to initiate the coagulation process.

A Novel Thrombelastograph?? Tissue Factor/Kaolin Assay of Activated Clotting Times for Monitoring Heparin Anticoagulation During Cardiopulmonary Bypass

We used a thrombelastograph (TEG) assay with tissue factor and kaolin (TEG TF/K) to measure activated clotting time (ACT) in 31 patients during cardiopulmonary bypass. For comparison, ACTs were also determined by a Hemochron Jr. Signature and a Hepcon HMS. The TEG TF/K correlated with both the Hepcon (r(2) = 0.789) and Hemochron (r(2) = 0.743) ACTs. The average ACT after heparin was 319 +/- 119 s (mean +/- sd) for the TEG TF/K compared with 624 +/- 118 s for the Hepcon instrument. To evaluate the effects of hemodilution on TEG TF/K and Hemochron assays, ACT assays were performed on blood diluted to 50% and titrated with heparin from 0 to 6 U/mL. Both instruments showed significant (P < 0.01) changes in the ACT-versus-heparin slope, but the 0 heparin intercept for the TEG TF/K ACTs was not significantly changed (P = 0.292), in contrast to that for the Hemochron device (P = 0.041). Both instruments also indicated the same 1.3:1 ratio of protamine to heparin for optimum heparin neutralization, with increasing ACTs at ratios >2.6:1. The TEG TF/K ACT assay rapidly monitors heparin anticoagulation, in addition to the capabilities of this instrument to monitor platelet function, clotting factors, and fibrinolysis.

Measurement of activated clotting time in children--comparison of the Celite i-STAT ACT with the Medtronic ACT II

BACKGROUND

To evaluate a recently introduced blood-saving method for the measurement of activated clotting time (ACT), the Celite i-STAT ACT, by comparing the values obtained with those from the widely used Medtronic ACT II device.

METHODS

In a prospective clinical study, we compared ACT values from the i-STAT device with the Medtronic ACT II device in 60 paediatric, interventional, cardiac catheterization procedures necessitating prophylactic heparinization. Blood samples were pair-analyzed using two i-STAT analyzers and one Medtronic ACT II device with double-tube-cartridges before and after heparinization. Data were compared using Bland-Altman bias analysis, Student's t-test and simple regression analysis.

RESULTS

Bias and precision between the Medtronic ACT II and the i-STAT ACT values was -5.4 +/- 26.3. The i-STAT and Medtronic ACT II values were similar before heparinization (P = 0.22), but i-STAT ACT values became significantly longer than Medtronic ACT II values after heparinization (P = 0.021). The increase of ACT after heparinization was greater (median 86.3; range 40-187 s) in the i-STAT analyzer than in the Medtronic ACT II analyzer (median 73.0; range 19-235.5 s). Increase in ACT values was inversely affected by intraoperative haemoglobin concentration in the Medtronic ACT II analyzer (P = 0.001) but not in the i-STAT analyzer.

CONCLUSION

Activated clotting times obtained from the Celite i-STAT ACT and the Medtronic ACT II demonstrated poor agreement. The technical principles are quite different and the two methods showed diverse susceptibility to intraoperative haemoglobin concentration. Users have to be aware of technique-specific ACT target ranges and their confounders, which need to be provided by the manufacturers.